Nozzles for steady flow chemical propulsion devices (ramjets, turojets, chemical rockets, etc.) are well known in the art. These devices expand high pressure exhaust gas from a combustor in a contained manner such that a pressure differential is established across the wall of the nozzle creating a net force acting along the nozzle axis, thereby increasing the momentum transferred to the engine from the combusted gas, generating additional thrust [Sutton, 1992][Mattingly et al., 1987]. Steady flow ejectors are also a well documented technology that has been used to augment the thrust created by a propulsion engine by entraining ambient air into the exhaust stream at the engine exit [Oates, 1989]. These steady ejectors are typically heavy and bulky when compared with the additional thrust generated, and therefore have found only limited application. Ejectors for single chamber, airbreathing, pulse deflagration devices (i.e., pulsejets) are also a well documented technology [Johnson, 1967][Lockwood, 1961][Lockwood, 1962]. These devices augment thrust of single chamber pulsed deflagration (pulsejet) combustors.
Relating to the current invention, it is important to understand that chemical propulsion devices may be divided into two classes: detonative and deflagrative combustion engines. In a pulse detonation engine, motive force is provided by expelling combustion products that result from a detonation process. The detonation process combusts reactants in a reaction zone which is coupled to a shockwave, the reaction zone releasing energy to sustain the shockwave, the shockwave enhancing combustion in the reaction zone. This coupled shockwave/reaction zone, commonly referred to as a detonation, propagates through the reactants at very high velocity compared to the propagation of a deflagrative reaction zone (a zone of combustion not coupled to a shock wave). Indeed, typical velocities are of the order of several thousands of feet per second for a detonation compared with a few tens of feet per second for a deflagration. The very high speed of the detonation forces combustion to occur very rapidly, increasing the thermodynamic efficiency of the process and, thus, explaining the motivation for a propulsion device based on this mode of combustion. One mode of operation for a pulse detonation engine is based on the detonative combustion of a fuel/oxidizer mixture in a combustion tube which is closed at one end and open at the other as detailed in U.S. Pat. No. 5,345,758 of T. R. Bussing. For this mode of operation, a detonation wave is initiated at the closed end of a tube filled with reactants consisting of one or more fuels and oxidizers which may be in gaseous, liquid, or solid form. The wave propagates at high velocity through the fuel/oxidizer mixture, producing very high pressure due to the rapid combustion. Forward thrust on the engine is produced as a result of the high pressure acting on the closed end of the tube. When the detonation wave reaches the open end of the tube, it produces a blast wave of high amplitude behind which the high pressure combustion products expel from the tube. The process of filling the tube with a detonable fuel/oxidizer mire and then producing a detonation can be repeated in a rapid manner (i.e., "pulsed") to produce a series of propulsive thrusts. It is the high pressure combusted gas exhausting from the open end of the combustion tube which is to be expanded in the nozzle of this invention in such a way as to maximize the momentum transfer from the exhaust gas to the engine as well as to enable the operation of other combustion tubes or fluid streams which may also be attached to the nozzle of this invention.
Propulsive devices which utilize deflagrative combustion are very well known and are typically used in commercial jet airliners, for instance. Indeed, all mass-produced propulsive devices which derive propulsive force from chemical combustion are based on deflagrative combustion. Deflagrative engines also include pulsejets which have a tube which has a set of reed valves (one-way valves) at one end, while being open at the other end. Operation is achieved by partially filling the combustion chamber with a combustible fuel/air mixture near the valved end, with the balance of the tube containing air drawn in from the open end. The combustion of the fuel/air mixture produces a moderate pressure wave which propels the combustion products and remaining air in the tube out of the open end. The over-expansion of the flow out of the open end then allows air to be drawn in through the one-way valves at the closed end and through the open end. Fuel is injected into the fresh air in the tube and the cycle is repeated. The repetition rate is controlled by the frequency of fuel injection and ignition can be self-sustaining once initiated with a spark device. Of importance is the detonative combusted gas exhausting from the open end of the combustion tube which is to be expanded in the nozzle of this invention in such a way as to maximize the momentum transfer from the exhaust gas to the engine as well as to enable the operation of other combustion tubes or fluid streams which may also be attached to the nozzle of this invention.